The invention relates to a target for testing perforating systems.
After a well has been drilled and casing has been cemented in the well, one or more portions of the casing adjacent pay zones are perforated to allow fluid from the surrounding formation to flow into the well for production to the surface. Perforating guns may be lowered into the well and the guns fired to create openings in the casing and to extend perforations into the surrounding formation. The firing of a perforating gun generally refers to exploding a shaped charge within a well. Several systems and techniques are available for firing perforating guns, including percussion-, pressure-, and electrically-actuated systems.
The characteristics (e.g., shape, diameter, depth, etc.) of the perforations created in the surrounding rock formation is a key determinant of well-flow performance. These characteristics may be referred to as the perforation characteristic of the rock formation, or of a simulated rock formation, whichever the case may be. To obtain data relating to such perforation characteristics, surface tests may be performed in which a perforating gun is fired into a test target representing the rock formation in the well where the gun will be fired. The most common type of perforating gun target is manufactured from concrete, such as the target defined by API RP 43, Edition 5, Section 1 ("API specification").
The concrete-type target is typically made from about 50% by volume sand. The API specification calls for sands to be used that qualify under ASTM Designation C33-67, which relates to the distribution of particle size in the sand, as shown below in Table 1.
TABLE 1 Percent Percent U.S. Mesh (mm) Passing Retained 3/8 in. 9.5 100 0 No. 4 4.8 95-100 0-5 No. 8 2.4 80-100 0-20 No. 16 1.2 50-85 15-50 No. 30 0.59 25-60 40-75 No. 50 0.30 10-30 70-90 No. 100 0.15 2-10 90-98 Pan &lt;0.15 0 100
In addition to use of a concrete-type target, another method of preparing a target for testing perforating guns is to obtain an actual sample of rock to represent the rock formation in the well ("down-hole rock formation"). To obtain this type of target, a near-surface or otherwise accessible rock formation must be located to represent the down-hole rock formation, and then a target sample must be quarried. This method of testing a perforating gun is substantially more expensive than constructing a concrete-type target. Also, depending on the availability and homogeneity of a given rock formation for constructing targets, it may be difficult under this method to reproduce testing results due to variation in the characteristics of the quarried rock formation.